This invention is concerned with a method of manufacture of a partially crosslinked olefinic thermoplastic elastomer (TPE) compositions.
Although compounds comprising a polyolefin and a partially crosslinked rubber possess good properties as TPEs such as heat resistance, mechanical strength, flexibility, and elasticity, their flow properties are inferior to those of common plastics, and this has limited their use in large molded parts owing to problems such as "flow marks." To improve these problems, for example, Japanese Pat. No. 54-23702 teaches the use of compounds consisting of polyolefin and two types of rubber, partially crosslinked, and Japanese Pat. No. 56-15743 teaches a compound in which a polyolefin is blended with a polyolefin/rubber blend that has been treated with organic peroxides. Also Japanese Pat. No. 56-15740 teaches the methods of manufacture of such compounds.
Japanese Application No. 60-188419 discloses compositions in which the rubber phase includes a halobutyl rubber, which is vulcanized with metal oxides (MOx) and/or Metal Chlorides (MCl) and partially crosslinked in the presence of a polyolefin, and then additional polyolefin is added.
Although such TPE compounds have excellent properties such as processability, low temperature impact, paintability, flexibility, and mechanical strength, their stiffness at elevated temperatures was less than adequate compared to polyurethane elastomers. It is one object of the present invention to improve high temperature stiffness of this type of TPE, without loss in the characteristics of olefinic TPEs.